钢桁梁全焊整体节点应力集中系数研究

Study on Stress Concentration Factor of Full-welded Integral Joint in Steel Truss Bridge

为探明全焊整体节点的疲劳性能,得到其应力集中系数计算公式并简化疲劳分析方法,首先验证了全焊整体节点的有限元模拟方法,分析了K型和KT型全焊整体节点在弦杆与腹杆平衡轴力、弦杆轴力、弦杆弯矩、腹杆平衡轴力等多种荷载工况下,斜腹杆与弦杆夹角、弦杆高度与圆弧板半径的比值、腹杆与弦杆厚度比对应力集中系数最大值的影响。结果表明:K型和KT型全焊整体节点应力集中系数有限元计算结果与单元类型和网格尺寸密切相关,建议选择C3D20R单元类型进行分析,提出了全局、腹杆和弦杆相贯线局部加密的方式;探明了几何无量纲参数对应力集中系数最大值的影响规律,并提出了K型和KT型全焊整体节点应力集中系数计算公式及应力集中系数最大值的计算公式,对比公式计算结果与有限元计算结果,其比值均值为1.012,均方差为0.034,变异系数为0.034,说明所提出公式具有较高的计算精度;采用应力集中系数计算公式进行实桥节点疲劳评估,计算得到中跨跨中节点最大热点应力幅为48.16 MPa,与有限元计算值44.04 MPa相差8.6%,说明该公式计算值偏大,但采用公式评估节点可得到偏安全结果。

In order to find out the fatigue performance of full-welded integral joint,the formula for calculating the stress concentration factor is obtained and the fatigue analysis method is simplified,the analysis of K-type and KT-type full-welded integral joints under various load conditions such as chord and web member balanced axial force,chord axial force,chord moment,web member balanced axial force,etc.,the influence of the angle between oblique web member and chord,the ratio of chord height to arc plate radius,and the ratio of web member to chord thickness on the maximum stress concentration factor is studied.The result shows that(1)the finite element calculation results of K-type and KT-type welded joints are closely related to the element type and the mesh size,it is suggested that the C3D20R element type should be selected for the analysis,a method of local encryption of the intersecting line of the whole,web member and chord is proposed;(2)the influence of geometric dimensionless parameters on the maximum value of stress concentration factor is discussed,and the formulas for calculating the stress concentration factor and the maximum value of stress concentration factor of K-type and KT-type welded joints are put forward,comparing the calculated results of the formula with those of the finite element method,the ratio mean value is 1.012,the mean square deviation is 0.034,and the factor of variation is 0.034,which shows that the proposed formula has higher calculation precision;(3)the stress concentration factor formula is used to evaluate the fatigue of actual bridge joints,and the maximum stress amplitude of the mid-span joint is 48.16 MPa,which is 8.6%different from the finite element calculation value of 44.04 MPa,it is shown that the calculated value of the formula is on the high side,but the partial safety result can be obtained by using the formula to evaluate the joints.